This invention relates to a control system for an offset printing machine.
As is well known, a number of process steps including ink kneading operation, a master plate feeding operation, an inking or ink forming operation, a transfer operation, a printing operation, and a master plate ejecting and cleaning operation must be executed for printing copies using a three-cylinder offset printing machine. A marker insertion operation may also be performed. When the printing machine is provided with an etching solution applicator, a master plate feeding and etching operation must be executed.
The aforementioned operational steps will be described in brief. A master plate, having an image formed thereon, is supplied by a plate feeding rubber roller and a plate feeding roller to a master cylinder in which the master plate is gripped at its leading end by the master cylinder and wound thereon. At the same time, an ink repellent etching solution is applied to the surface of the master plate, by an etching roller of an etching solution application, so that non-image regions of the plate will have affinity for water and image regions thereof will have affinity for oil (plate feeding and etching operation). At this time, inking rollers are moved away from the master cylinder, and an ink kneading step, in which ink is mixed with water and kneaded, is carried out by a set of ink forming rollers.
Following the etching operation, ink is applied to the surface of the plate by the inking roller (inking operation). An ink image formed on the plate in the inking operation is transferred onto a blanket cylinder (transfer operation). A sheet, on which the image is to be formed, is fed, by a sheet feeding roller and feeding roller, between the blanket cylinder and an impression cylinder, so that the image of the plate will be printed on the copy sheet (printing operation). When a predetermined number of copies of the plate image are produced, the master plate wound on the master cylinder is removed and ejected by means of plate ejecting rollers, and the surface of the blanket cylinder is cleaned to remove therefrom the ink image of the plate (plate ejecting and cleaning operation). One sheet only is then passed between the blanket cylinder and the impression cylinder so as to mark the different sets of copies (mark insertion operation).
Heretofore, a control shaft which can be stopped mechanically at a number of angular positions (control positions) for switching the operation of a offset printing machine between the various operations has been used to control the operation of the offset printing machine. The control shaft is operated by a click mechanism which moves the shaft stepwise to a desired control position, in order to thereby effect changeover of the operational processes. In this control method, the operator manually operates a lever so that the various printing operations will be executed in a predetermined order while the operator checks, for example, the number of revolutions of the master cylinder. Difficulties have hitherto been experienced in obtaining a full understanding by the operator of the complicated operations of an offset printing machine. Since the number of revolutions of the master cylinder is counted by the operator, there has been a variation from one operator to another in the period of time required for controlling the printing processes. Moreover, there have often been cases where it is difficult to determine the source of trouble when misoperation occurs during the printing processes.
Proposals have been made to use a sequence control system for controlling the printing processes of an offset printing machine. Such sequence control system uses relays, timers and other elements for sequentially programming the successive printing processes. This system has the disadvantages that it is difficult to switch the machine from automatic operation to manual operation, and that difficulties are encountered in putting back the machine to one of the operation processes which have already been executed, while the processes are being executed in chronological sequence. Additional disadvantages of this system are that the parts are large in number and the mechanism is complex. Therefore, it has been impossible to obtain a control system of high precision in performance, low cost and simple mechanism, when sequence control mechanism is incorporated in the control system.